Auto merge of #118460 - the8472:fix-vec-realloc, r=saethlin

Fix in-place collect not reallocating when necessary

Regression introduced in rust-lang/rust#110353.
This was [caught by miri](https://rust-lang.zulipchat.com/#narrow/stream/269128-miri/topic/Cron.20Job.20Failure.20.28miri-test-libstd.2C.202023-11.29/near/404764617)

r? `@saethlin`

Author: bors